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Copyright (C) 2015 Freescale Semiconductor Inc.
DPAA2 (Data Path Acceleration Architecture Gen2)
------------------------------------------------
This document provides an overview of the Freescale DPAA2 architecture
and how it is integrated into the Linux kernel.
Contents summary
-DPAA2 overview
-Overview of DPAA2 objects
-DPAA2 Linux driver architecture overview
-bus driver
-dprc driver
-allocator
-dpio driver
-Ethernet
-mac
DPAA2 Overview
--------------
DPAA2 is a hardware architecture designed for high-speeed network
packet processing. DPAA2 consists of sophisticated mechanisms for
processing Ethernet packets, queue management, buffer management,
autonomous L2 switching, virtual Ethernet bridging, and accelerator
(e.g. crypto) sharing.
A DPAA2 hardware component called the Management Complex (or MC) manages the
DPAA2 hardware resources. The MC provides an object-based abstraction for
software drivers to use the DPAA2 hardware.
The MC uses DPAA2 hardware resources such as queues, buffer pools, and
network ports to create functional objects/devices such as network
interfaces, an L2 switch, or accelerator instances.
The MC provides memory-mapped I/O command interfaces (MC portals)
which DPAA2 software drivers use to operate on DPAA2 objects:
+--------------------------------------+
| OS |
| DPAA2 drivers |
| | |
+-----------------------------|--------+
|
| (create,discover,connect
| config,use,destroy)
|
DPAA2 |
+------------------------| mc portal |-+
| | |
| +- - - - - - - - - - - - -V- - -+ |
| | | |
| | Management Complex (MC) | |
| | | |
| +- - - - - - - - - - - - - - - -+ |
| |
| Hardware Hardware |
| Resources Objects |
| --------- ------- |
| -queues -DPRC |
| -buffer pools -DPMCP |
| -Eth MACs/ports -DPIO |
| -network interface -DPNI |
| profiles -DPMAC |
| -queue portals -DPBP |
| -MC portals ... |
| ... |
| |
+--------------------------------------+
The MC mediates operations such as create, discover,
connect, configuration, and destroy. Fast-path operations
on data, such as packet transmit/receive, are not mediated by
the MC and are done directly using memory mapped regions in
DPIO objects.
Overview of DPAA2 Objects
-------------------------
The section provides a brief overview of some key objects
in the DPAA2 hardware. A simple scenario is described illustrating
the objects involved in creating a network interfaces.
-DPRC (Datapath Resource Container)
A DPRC is an container object that holds all the other
types of DPAA2 objects. In the example diagram below there
are 8 objects of 5 types (DPMCP, DPIO, DPBP, DPNI, and DPMAC)
in the container.
+---------------------------------------------------------+
| DPRC |
| |
| +-------+ +-------+ +-------+ +-------+ +-------+ |
| | DPMCP | | DPIO | | DPBP | | DPNI | | DPMAC | |
| +-------+ +-------+ +-------+ +---+---+ +---+---+ |
| | DPMCP | | DPIO | |
| +-------+ +-------+ |
| | DPMCP | |
| +-------+ |
| |
+---------------------------------------------------------+
From the point of view of an OS, a DPRC is bus-like. Like
a plug-and-play bus, such as PCI, DPRC commands can be used to
enumerate the contents of the DPRC, discover the hardware
objects present (including mappable regions and interrupts).
dprc.1 (bus)
|
+--+--------+-------+-------+-------+
| | | | |
dpmcp.1 dpio.1 dpbp.1 dpni.1 dpmac.1
dpmcp.2 dpio.2
dpmcp.3
Hardware objects can be created and destroyed dynamically, providing
the ability to hot plug/unplug objects in and out of the DPRC.
A DPRC has a mappable mmio region (an MC portal) that can be used
to send MC commands. It has an interrupt for status events (like
hotplug).
All objects in a container share the same hardware "isolation context".
This means that with respect to an IOMMU the isolation granularity
is at the DPRC (container) level, not at the individual object
level.
DPRCs can be defined statically and populated with objects
via a config file passed to the MC when firmware starts
it. There is also a Linux user space tool called "restool"
that can be used to create/destroy containers and objects
dynamically.
-DPAA2 Objects for an Ethernet Network Interface
A typical Ethernet NIC is monolithic-- the NIC device contains TX/RX
queuing mechanisms, configuration mechanisms, buffer management,
physical ports, and interrupts. DPAA2 uses a more granular approach
utilizing multiple hardware objects. Each object has specialized
functions, and are used together by software to provide Ethernet network
interface functionality. This approach provides efficient use of finite
hardware resources, flexibility, and performance advantages.
The diagram below shows the objects needed for a simple
network interface configuration on a system with 2 CPUs.
+---+---+ +---+---+
CPU0 CPU1
+---+---+ +---+---+
| |
+---+---+ +---+---+
DPIO DPIO
+---+---+ +---+---+
\ /
\ /
\ /
+---+---+
DPNI --- DPBP,DPMCP
+---+---+
|
|
+---+---+
DPMAC
+---+---+
|
port/PHY
Below the objects are described. For each object a brief description
is provided along with a summary of the kinds of operations the object
supports and a summary of key resources of the object (mmio regions
and irqs).
-DPMAC (Datapath Ethernet MAC): represents an Ethernet MAC, a
hardware device that connects to an Ethernet PHY and allows
physical transmission and reception of Ethernet frames.
-mmio regions: none
-irqs: dpni link change
-commands: set link up/down, link config, get stats,
irq config, enable, reset
-DPNI (Datapath Network Interface): contains TX/RX queues,
network interface configuration, and rx buffer pool configuration
mechanisms.
-mmio regions: none
-irqs: link state
-commands: port config, offload config, queue config,
parse/classify config, irq config, enable, reset
-DPIO (Datapath I/O): provides interfaces to enqueue and dequeue
packets and do hardware buffer pool management operations. For
optimum performance there is typically DPIO per CPU. This allows
each CPU to perform simultaneous enqueue/dequeue operations.
-mmio regions: queue operations, buffer mgmt
-irqs: data availability, congestion notification, buffer
pool depletion
-commands: irq config, enable, reset
-DPBP (Datapath Buffer Pool): represents a hardware buffer
pool.
-mmio regions: none
-irqs: none
-commands: enable, reset
-DPMCP (Datapath MC Portal): provides an MC command portal.
Used by drivers to send commands to the MC to manage
objects.
-mmio regions: MC command portal
-irqs: command completion
-commands: irq config, enable, reset
Object Connections
------------------
Some objects have explicit relationships that must
be configured:
-DPNI <--> DPMAC
-DPNI <--> DPNI
-DPNI <--> L2-switch-port
A DPNI must be connected to something such as a DPMAC,
another DPNI, or L2 switch port. The DPNI connection
is made via a DPRC command.
+-------+ +-------+
| DPNI | | DPMAC |
+---+---+ +---+---+
| |
+==========+
-DPNI <--> DPBP
A network interface requires a 'buffer pool' (DPBP
object) which provides a list of pointers to memory
where received Ethernet data is to be copied. The
Ethernet driver configures the DPBPs associated with
the network interface.
Interrupts
----------
All interrupts generated by DPAA2 objects are message
interrupts. At the hardware level message interrupts
generated by devices will normally have 3 components--
1) a non-spoofable 'device-id' expressed on the hardware
bus, 2) an address, 3) a data value.
In the case of DPAA2 devices/objects, all objects in the
same container/DPRC share the same 'device-id'.
For ARM-based SoC this is the same as the stream ID.
DPAA2 Linux Driver Overview
---------------------------
This section provides an overview of the Linux kernel drivers for
DPAA2-- 1) the bus driver and associated "DPAA2 infrastructure"
drivers and 2) functional object drivers (such as Ethernet).
As described previously, a DPRC is a container that holds the other
types of DPAA2 objects. It is functionally similar to a plug-and-play
bus controller.
Each object in the DPRC is a Linux "device" and is bound to a driver.
The diagram below shows the Linux drivers involved in a networking
scenario and the objects bound to each driver. A brief description
of each driver follows.
+------------+
| OS Network |
| Stack |
+------------+ +------------+
| Allocator |. . . . . . . | Ethernet |
|(dpmcp,dpbp)| | (dpni) |
+-.----------+ +---+---+----+
. . ^ |
. . <data avail, | |<enqueue,
. . tx confirm> | | dequeue>
+-------------+ . | |
| DPRC driver | . +---+---V----+ +---------+
| (dprc) | . . . . . .| DPIO driver| | MAC |
+----------+--+ | (dpio) | | (dpmac) |
| +------+-----+ +-----+---+
|<dev add/remove> | |
| | |
+----+--------------+ | +--+---+
| mc-bus driver | | | PHY |
| | | |driver|
| /fsl-mc@80c000000 | | +--+---+
+-------------------+ | |
| |
================================ HARDWARE =========|=================|======
DPIO |
| |
DPNI---DPBP |
| |
DPMAC |
| |
PHY ---------------+
===================================================|========================
A brief description of each driver is provided below.
mc-bus driver
-------------
The mc-bus driver is a platform driver and is probed from an
"/fsl-mc@xxxx" node in the device tree passed in by boot firmware.
It is responsible for bootstrapping the DPAA2 kernel infrastructure.
Key functions include:
-registering a new bus type named "fsl-mc" with the kernel,
and implementing bus call-backs (e.g. match/uevent/dev_groups)
-implemeting APIs for DPAA2 driver registration and for device
add/remove
-creates an MSI irq domain
-do a device add of the 'root' DPRC device, which is needed
to bootstrap things
DPRC driver
-----------
The dprc-driver is bound DPRC objects and does runtime management
of a bus instance. It performs the initial bus scan of the DPRC
and handles interrupts for container events such as hot plug.
Allocator
----------
Certain objects such as DPMCP and DPBP are generic and fungible,
and are intended to be used by other drivers. For example,
the DPAA2 Ethernet driver needs:
-DPMCPs to send MC commands, to configure network interfaces
-DPBPs for network buffer pools
The allocator driver registers for these allocatable object types
and those objects are bound to the allocator when the bus is probed.
The allocator maintains a pool of objects that are available for
allocation by other DPAA2 drivers.
DPIO driver
-----------
The DPIO driver is bound to DPIO objects and provides services that allow
other drivers such as the Ethernet driver to receive and transmit data.
Key services include:
-data availability notifications
-hardware queuing operations (enqueue and dequeue of data)
-hardware buffer pool management
There is typically one DPIO object per physical CPU for optimum
performance, allowing each CPU to simultaneously enqueue
and dequeue data.
The DPIO driver operates on behalf of all DPAA2 drivers
active in the kernel-- Ethernet, crypto, compression,
etc.
Ethernet
--------
The Ethernet driver is bound to a DPNI and implements the kernel
interfaces needed to connect the DPAA2 network interface to
the network stack.
Each DPNI corresponds to a Linux network interface.
MAC driver
----------
An Ethernet PHY is an off-chip, board specific component and is managed
by the appropriate PHY driver via an mdio bus. The MAC driver
plays a role of being a proxy between the PHY driver and the
MC. It does this proxy via the MC commands to a DPMAC object.